[FLINK-29775][tests][JUnit5 migration] Module: flink-statebackend-rocksdb

[spuru9]

What is the purpose of the change

Migrates the remaining JUnit 4 tests in flink-statebackend-rocksdb to JUnit 5 and converts their assertions to AssertJ, as part of FLINK-25325.

Most tests in this module have a near-identical sibling in flink-statebackend-forst, which was migrated in FLINK-39767 (6627acb). Where a sibling exists, this PR follows it so the two modules stay consistent, except where noted below.

After this change the module has no reference to org.junit.* (outside org.junit.jupiter), no Hamcrest matchers, and no TestLogger.

Brief change log

• @Rule / @ClassRule TemporaryFolder → @TempDir. A test that needs a single directory takes it as a method parameter (@TempDir File dir). TempDirUtils.newFolder(root) is kept only where one test method needs several distinct directories: RocksDBIncrementalCheckpointUtilsTest.testClipDBWithKeyGroupRange calls its helper nine times and each call opens its own RocksDB instance, and RocksDBKeyedStateBackendTestFactory.create(...) hands out a fresh directory per call.
• @RunWith(Parameterized.class) → native @ParameterizedTest + @ValueSource(booleans = {false, true}) in RocksIncrementalCheckpointRescalingTest. This deviates from ForStIncrementalCheckpointRescalingTest, which uses ParameterizedTestExtension + @TestTemplate: the parameter here is a single boolean, so the native form is enough and needs no @Parameters factory.
• @Test(expected = ...) and the manual try { ...; fail(); } catch (X e) { ... } blocks → assertThatThrownBy(...) / assertThatCode(...).doesNotThrowAnyException().
• org.junit.Assert and Hamcrest matchers → AssertJ, preferring the native idioms (hasSize, containsExactly, containsExactlyInAnyOrderElementsOf, hasToString, hasBinaryContent, exists/doesNotExist/isEmptyDirectory, allMatch, satisfiesAnyOf, cause().isSameAs, hasMessageContaining). Sorting a collection just to compare it element by element is replaced by an order-agnostic content assertion. For type checks the conversion keeps the original strictness: isExactlyInstanceOf where the original compared getClass(), isInstanceOf where it used instanceof or Hamcrest instanceOf.
• org.junit.Assume → AssertJ's Assumptions.assumeThat(...), so these files do not mix JUnit 5 and AssertJ assumptions.
• Dropped extends TestLogger and the now-unnecessary public modifiers on test classes and methods. RocksDBExtension stays public because it is used across packages, from snapshot/RocksIncrementalSnapshotStrategyTest and sstmerge/CompactionTaskProducerTest. Logging behaviour is unchanged: the root pom enables junit.jupiter.extensions.autodetection.enabled, and TestLoggerExtension is registered by the flink-runtime and flink-streaming-java test-jars this module already depends on.
• RocksDBExtension and RocksDBKeyedStateBackendTestFactory are test utilities rather than tests, but were still holding a JUnit 4 TemporaryFolder. RocksDBExtension (itself a JUnit 5 extension, so it cannot use @TempDir injection) now creates and deletes its own temp directory; RocksDBKeyedStateBackendTestFactory.create(...) takes a java.nio.file.Path instead.

Assertion messages were kept via .as(...). The ones that disappear are fail("...should have thrown")-style messages, which assertThatThrownBy expresses natively, and messages whose content AssertJ already prints (e.g. assertThat(errorRef.get()).isNull() prints the throwable).

Verifying this change

This change is a test-only rework; it is verified by the existing tests it migrates.

mvn verify -pl flink-state-backends/flink-statebackend-rocksdb passes with the same number of tests before and after, and the per-class counts are unchanged as well:

• before: 843 unit tests (9 skipped) + 2 integration tests
• after: 843 unit tests (9 skipped) + 2 integration tests

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no

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Was generative AI tooling used to co-author this PR?

• Yes (Claude Code)

Generated-by: Claude Code (claude-opus-5)

[flinkbot]

CI report:

• 2468e39 Azure: SUCCESS

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[spuru9]

extends TestLoggeris dropped without adding aMETA-INF/servicesfile —TestLoggerExtensionis already auto-registered from theflink-streaming-java` test-jar this module depends on.

[spuru9]

keeps TempDirUtils.newFolder(tmp) because testClipDBWithKeyGroupRangeHelper is called 9× from one test method

[spuru9]

@snuyanzin Can you review this, there was no activity in the JIRA for over a year with no open PR as well.